Method of obtaining a range of colors

ABSTRACT

A method of obtaining a range of colors includes the following steps:  
     selecting a test color from a predetermined set of colors,  
     selecting a test palette comprising a plurality of color samples,  
     measuring the real color of each sample when illuminated by a white light source,  
     measuring the apparent color of each sample when illuminated by a test source formed by the white light source filtered by the test color,  
     measuring the chromatic error between the real color and the apparent color of each sample, taking account of chromatic adaptation,  
     measuring the mean chromatic error for all the chromatic errors,  
     comparing the mean chromatic error to a test value, and  
     adding the test color to the range if the mean chromatic error is less than or equal to the test value.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a method of obtaining a range of colors, in particular for fabricating colored ophthalmic lenses.

[0003] 2. Description of the Prior Art

[0004] The choice of colored lenses used to be dictated by the desire of the wearer to reduce perceived glare, in particular in order to relieve the retina in bright sunlight.

[0005] Responding to fashion trends, today's wearers are turning to ophthalmic lenses whose color is chosen merely as a matter of taste, and generally independently of their capacity to reduce glare.

[0006] Opticians' displays are therefore featuring more and more so-called “sunglasses”, although this name is now not appropriate, with lenses of increasingly varied colors: yellow, green, blue, red, etc.

[0007] Wearing colored ophthalmic lenses modifies the colors perceived by the wearer, even if the wearer adapts naturally to the color of the lenses.

[0008] At present, the manufacture of a colored ophthalmic lens takes account only of its final intrinsic appearance, without concern as to the effect of wearing it on the modified appearance of colors.

[0009] The invention aims to overcome this insufficiency by proposing a method of obtaining a range of colors which, when applied in particular to fabricating a colored ophthalmic lens, takes account of its effect on the modified appearance of colors.

SUMMARY OF THE INVENTION

[0010] To this end, a first aspect of the invention proposes a method of obtaining a range of colors, including the following steps:

[0011] selecting a test color from a predetermined set of colors,

[0012] selecting a test palette comprising a plurality of color samples,

[0013] measuring the real color of each sample when illuminated by a white light source,

[0014] measuring the apparent color of each sample when illuminated by a test source formed by the white light source filtered by the test color,

[0015] measuring the chromatic error between the real color and the apparent color of each sample, taking account of chromatic adaptation,

[0016] measuring the mean chromatic error for all the chromatic errors,

[0017] comparing the mean chromatic error to a test value, and

[0018] adding the test color to the range if the mean chromatic error is less than or equal to the test value.

[0019] In one embodiment of the invention the test color is added to the range if and only if each chromatic error is less than or equal to the test value.

[0020] In another embodiment of the invention the method includes the following steps if at least one chromatic error is greater than the test value:

[0021] measuring the angular distribution of the calorimetric deviations between the real color and the apparent color of each sample, and

[0022] adding the test color to the range if the angular distribution is uniform.

[0023] The set comprises the Munsell atlas, for example, and the test palette comprises a plurality of color samples chosen from the Munsell atlas, or a plurality of samples whose colors are most representative of the Munsell space.

[0024] The apparent color and the real color are measured by calculating their coordinates in a predetermined chromatic space, such as the CIELAB space.

[0025] A second aspect of the invention provides a range of more than two colors obtained by the above method.

[0026] A third aspect of the invention provides a method of obtaining a colored ophthalmic lens, including a step of selecting a color from the above range or obtained by the above method.

[0027] Other features and advantages of the invention will become apparent in the light of the following description of one embodiment of the invention, which is given by way of non-limiting example and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a diagrammatic view showing a palette comprising a plurality of color samples illuminated by a white source and viewed by an observer.

[0029]FIG. 2 is a diagrammatic view showing one of the samples from the FIG. 1 palette, illuminated by the same white source, with a colored lens between the observer and the palette.

[0030]FIG. 3 is a view similar to FIG. 1, with the colored lens from FIG. 2 between the palette and the observer.

[0031]FIG. 4 is a view similar to FIG. 3 with the lens between the white source and the palette.

[0032]FIG. 5 is a graph representing the spectral energy distribution of the D₆₅ light source.

[0033]FIG. 6 is a graph showing the transmission factor of a blue lens as a function of the wavelength of the incident light.

[0034]FIG. 7 is a cylindrical diagrammatic representation of the Munsell space.

[0035]FIG. 8 is a graph representing the reflection factor of six color samples as a function of the wavelength of the incident light with which they are illuminated.

[0036]FIG. 9 is a graph representing the reflection factor of three color samples as a function of the wavelength of the incident light with which they are illuminated.

[0037]FIG. 10 is a representation of a plane chromatic space a* b* showing, by circles, the so-called real colors of the six samples from FIG. 8, when illuminated by a white source, and, by crosses, the so-called apparent colors of the six samples when illuminated by a test source formed by the filtered white source; the calorimetric deviation vectors linking the circle and the cross relating to each color are also shown in this chromatic space.

[0038]FIG. 11 is a representation of a plane chromatic space a* b* showing, by circles, the so-called real colors of 127 samples when illuminated by a white source and, by crosses, the so-called apparent colors of the 127 samples when illuminated by a test source formed by the filtered white source.

[0039]FIG. 12 is a diagram showing steps of a method according to the invention.

[0040]FIGS. 13, 14 and 15 are graphs representing the spectral distributions of the transmission factors of three colored lenses.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041]FIG. 1 shows a palette P comprising a plurality of samples E1, E2, E3 of respective different real colors C1, C2, C3.

[0042] When the palette P is illuminated by a white light source S that is supposedly ideal, i.e. similar to natural daylight, for example in sunshine or under a cloudless sky, in the north, an observer O, also supposedly ideal, i.e. suffering from no chromatic aberrations or ametropia, who is viewing the palette 2, perceives a representation thereof, referred to as the perceived palette, whose samples represent respective colors identical to the real colors C1, C2, C3 of the samples E1, E2, E3.

[0043] If a colored ophthalmic lens V of color C is placed between the observer O and any one of the samples E1, E2 or E3 of the palette P, that sample assumes for the observer O a color C′1, C′2, C′3 different from its real color (FIG. 2).

[0044] On the other hand, if the same colored ophthalmic lens V is placed between the observer O and the whole of the palette P (FIG. 3), each sample has for the observer a color C″1, C″2, C″3 that is not only different from its real color but also from the perceived color C′1, C′2, C′3 when the lens V is placed in front of only one sample E1, E2 or E3.

[0045] Accordingly, for the observer O, the distortion of the colors caused by the lens V for each sample E1, E2, E3 varies as a function of the visual area covered by the lens V. This is explained by the chromatic adaptation faculties of the visual system of the observer O, comparable to a balance of whites. The change from the real colors C1, C2, C3 to the perceived colors C″1, C″2, C″3 due to the colored lens is called calorimetric deviation.

[0046] At present, when choosing colored ophthalmic lenses, the calorimetric deviation is left to the judgement of the wearer, and is therefore subjective, even though some lens colors can cause a calorimetric deviation that is objectively unacceptable, in particular in the case of perception of colors conforming to a code or a standard, for example in connection with safety signals.

[0047] The aim is to draw up a range of colors that can be used for the manufacture of ophthalmic lenses whose effect on calorimetric deviation when employed to filter a predefined white light source is acceptable in accordance with objective criteria that emerge hereinafter.

[0048] Note first of all that, for the observer, whether the lens is between the source and the palette or between the palette and the observer is immaterial.

[0049] Consequently, placing the lens V between the palette P and the observer O has the same effect as illuminating the palette P with a colored source SF formed by the white source S filtered by the colored lens V (FIG. 4). The filtered source is referred to as the test source hereinafter.

[0050] Provided that the chromatic adaptation faculties of the visual system are taken into account, it is therefore possible to obtain the required range of colors by a method that does not necessitate the intervention of an observer.

[0051] A first step consists of choosing the test source, that is to say, on the one hand, the white source and, on the other hand, the color employed to filter it, which is referred to as the test color hereinafter.

[0052] The white source is chosen from ideal white sources. In a preferred embodiment of the invention, the white source is the D₆₅ light source defined by the International Commission on Illumination, which is well-known to the person skilled in the art and has a color temperature equal to approximately 6 500 K.

[0053] The test color is chosen from a set of predetermined colors that are preferably representative of all the colors of the visible spectrum. In one embodiment of the invention, this set is the Munsell color atlas, which takes the form of a cylindrical array in which the colors are classified in accordance with the following three criteria: hue, value and chroma. FIG. 7 is a cylindrical diagrammatic representation of the Munsell atlas, which is well-known to the person skilled in the art.

[0054] The atlas provides more than a thousand color samples (in fact 1 269 samples).

[0055] Each sample, and consequently each color, from the Munsell atlas can be characterized by the spectral distribution of its transmission factor, i.e. the spectral distribution of the transmission factor of a lens of the color concerned. This distribution comprises all of the transmission factors of the colored lens for a range of wavelengths from 350 nm to 750 nm, which corresponds closely to the spectrum visible to the human eye (1 nm=10⁻⁹ m).

[0056] The transmission factor of a given object (in this instance the lens) when illuminated by an incident luminous flux is a dimensionless magnitude with a value from 0 to 1, or from 0% to 100% if expressed as a percentage, equal to the ratio of the transmitted luminous flux to the incident luminous flux (multiplied by a factor of 100 if expressed as a percentage).

[0057] Accordingly, for a step of 1 nm, each sample, and consequently the corresponding color, can be characterized by a set of 401 reflection factors. For each color, it is therefore possible to construct from this set a curve representing the spectral distribution of its reflection factor, as shown in FIGS. 6, 13, 14 and 15, for blue, gray, green and brown colors, respectively.

[0058] Using the white source and the chosen test color, it is then possible to characterize the test source: from the spectral energy distribution E₆₅(λ) of the white light source (in this instance the D₆₅ light source, see FIG. 5) and the spectral transmission factor τ(λ) of the test color, the spectral energy distribution E_(K)(λ) of the test source is determined, this energy being equal to the product of the energy E₆₅(λ) of the white light source and the transmission factor τ(λ) associated with the test color:

E _(K)(λ)=τ(λ) E ₆₅ (λ)

[0059] The next step is to calculate, taking account of chromatic adaptation, the calorimetric deviation caused by the test source on a palette referred to hereinafter as the test palette, comprising a plurality of color samples that are sufficiently representative of the whole of the visible spectrum, in order to model visual situations that an observer is likely to encounter in daily life.

[0060] The test palette can be based on the Munsell atlas, which conforms to this requirement.

[0061] As stated above, each sample, and consequently each color, from the Munsell atlas can be characterized by the spectral distribution of its transmission factor.

[0062] Each sample, respectively each color, can also be characterized by the spectral distribution of its reflection factor. This distribution comprises all of the reflection factors of the sample for a range of wavelengths from 350 nm to 750 nm, for example, which correspond closely to the spectrum visible to the human eye (1 nm=10⁻⁹ m).

[0063] The reflection factor of a given sample illuminated by an incident luminous flux is a dimensionless magnitude from 0 to 1, or from 0% to 100% if expressed as a percentage, and equal to the ratio of the reflected luminous flux to the incident luminous flux, multiplied by a factor of 100 if expressed as a percentage.

[0064] The number of reflection factors characteristic of each sample depends on the chosen step between two adjacent wavelengths in the range of wavelengths.

[0065] Accordingly, for a step of 5 nm, each sample is characterized by a set of 81 reflection factors.

[0066] For a wavelength step of 5 nm, the Munsell atlas can therefore be represented algebraically by a Munsell matrix X comprising 1 269 rows and 81 columns, each row corresponding to a sample and containing all of the reflection factors thereof for the chosen range.

[0067] These reflection factors can be measured directly by spectrophotometry, but the person skilled in the art can obtain their values from the Computer Science and Physics Department of the University of Joensuu, Finland.

[0068] Of course, the Munsell space could itself constitute the test palette. However, given the size of the Munsell matrix X, this implies very long computations, requiring very costly data processing or electronic systems.

[0069] It is therefore preferable to employ a test palette of reduced size. Let N denote the number of samples on the test palette, each sample and its corresponding color being both identified by an integer index i from 1 to N.

[0070] Accordingly, in a first embodiment of the invention, the test palette comprises 127 samples (N=127) extracted from the Munsell atlas by selecting one sample in ten. Of course, it would be possible to select one sample in five, for example, or, conversely, one sample in twenty, depending on the available computation power.

[0071] In a second embodiment of the invention, the test palette is constructed by compressing the Munsell atlas in order to extract the most significant color tendencies.

[0072] This compression is effected by reducing the Munsell matrix X using the method known as principal component analysis (PCA).

[0073] The PCA method includes the following steps:

[0074] calculating a correlation matrix C equal to the product of the transposed matrix ^(t)X of the calculation matrix X by the matrix X itself:

C=^(t)XX,

[0075]  and

[0076] calculating the eigenvalues and eigenvectors of the correlation matrix C, which is symmetrical by definition.

[0077] Each eigenvector, which takes the form of a column of 81 components each corresponding to a wavelength, is representative of an eigencolor.

[0078] The test palette can comprise a set of 81 samples (N=81) in which the color of each sample is a respective eigencolor.

[0079] The eigenvalue associated with each of the eigencolors corresponds to its inertia, i.e. the representativeness of the eigencolor with respect to all of the colors from the Munsell atlas.

[0080] For each eigencolor i, the weight Wi of its eigenvalue α₁ is given by the following equation: $W_{i} = \frac{\alpha_{i}}{\sum\limits_{i = 1}^{N}\quad \alpha_{i}}$

[0081] The test palette can equally comprise a subset of samples whose colors are chosen from the eigencolors of higher weight.

[0082] To this end, the eigenvectors are classified in decreasing order of their respective eigenvalues, i.e. from the eigenvector having the highest eigenvalue to the eigenvector having the lowest eigenvalue.

[0083] It is found that the first six eigenvectors taken together account for approximately 80% of the total inertia of all of the eigenvectors, and that consequently the first six eigenvectors provide an acceptable representation of the color tendencies of the Munsell atlas.

[0084] The first six eigenvectors are therefore selected, i.e. the six eigenvectors having the highest eigenvalues (N=6).

[0085] The test palette therefore comprises six colors with the highest weights: it can be represented, algebraically, by a matrix constituted by juxtaposing six associated eigenvectors.

[0086] The FIG. 8 graph shows these first six eigenvectors, in the form of curves of the type R=f(λ), where R is the reflection factor and λ is the wavelength.

[0087] As is clear from this figure, the eigencolors corresponding to the first six eigenvectors are pastel colors.

[0088] Note that for each wavelength λ, it is possible to arrive at an approximation of the reflection factor of each sample from the Munsell atlas on the basis of the first six eigenvectors, using the following equation: $\begin{matrix} {{R(\lambda)} = {\sum\limits_{i = 1}^{i = N}\quad {\sqrt{\alpha_{i}}{W_{i}\left( \alpha_{i} \right)}{V_{i}(\lambda)}}}} & (1) \end{matrix}$

[0089] in which λ is the wavelength concerned, V_(i)(λ) the component of the i^(th) eigenvector for the wavelength λ, α_(i) the associated eigenvalue and W_(i) the weight thereof.

[0090] The FIG. 9 graph shows, in full line and in dashed line, the curves of the reflection factors of three color samples from the Munsell atlas as a function of the wavelength of the incident light, these factors being obtained by means of the above equation (1), respectively with N=6 and N=81, and shows that reflection factors corresponding to N=6 are an acceptable approximation of the reflection factors corresponding to N=81.

[0091] Once the test palette has been constructed, the real color of each of its samples is measured, in other words the color of the sample when illuminated by a white light source, in this instance the D₆₅ light source, after which its apparent color is measured, i.e. its color when illuminated by the test source.

[0092] In a preferred embodiment of the invention, these measurements are effected at least in part using the International Commission on Illumination CRI-96 method.

[0093] The calculations carried out to measure the apparent color of a given sample i include the following steps:

[0094] a) Calculating trichromatic coordinates (X_(k), Y_(k), Z_(k)) of the test source in the space CIEXYZ, as defined by the International Commission on Illumination, from its relative spectral energy distribution E_(k)(λ), as defined above;

[0095] b) Calculating trichromatic coordinates in the space CIEXYZ of the white light source which is chosen so that its chromaticity is as close as possible to the chromaticity of the test source, which in this instance is the D₆₅ light source;

[0096] c) Calculating trichromatic coordinates (X_(i), Y_(i), Z_(i)) in the space CIEXYZ of the color i when illuminated by the test source;

[0097] d) Converting from the trichromatic coordinates X_(i), Y_(i), Z_(i) of the system CIEXYZ to the spectral coordinates R_(i), G_(i), B_(i) of the RGB system, as defined by the International Commission on Illumination, using the following equations:

R ₁=0.040024X _(i)+0.70760Y _(i)−0.0808Z _(i)

G ₁=−0.22630X _(i)+1.16532Y _(i)+0.04570Z _(i)

B _(i)=0.91822Z _(i)

[0098] e) Converting the test source into a reference source and calculating, for the color when illuminated by the reference source, its spectral coordinates R_(D1), G_(Di), B_(Di) in the RGB system: $\begin{matrix} {R_{Di} = {{\left( {{20\xi_{D}} + 1} \right)\left\lbrack \frac{R_{i} + 1}{{20\xi} + 1} \right\rbrack}^{\frac{\beta_{1}{(R_{0})}}{\beta_{1}{(R_{0D})}}} - 1}} \\ {G_{Di} = {{\left( {{20\eta_{D}} + 1} \right)\left\lbrack \frac{G_{i} + 1}{{20\eta} + 1} \right\rbrack}^{\frac{\beta_{1}{(G_{0})}}{\beta_{1}{(G_{0D})}}} - 1}} \\ {B_{Di} = {{\left( {{20\zeta_{D}} + 1} \right)\left\lbrack \frac{B_{i} + 1}{{20\zeta} + 1} \right\rbrack}^{\frac{\beta_{2}{(B_{0})}}{\beta_{2}{(B_{0D})}}} - 1}} \end{matrix}$ in  which: $\begin{matrix} {\xi = \quad \frac{{0.48105X_{k}} + {0.78841Y_{k}} - 0.08081}{Y_{k}}} \\ {\eta = \quad \frac{{{- 0.27200}X_{k}} + {1.11962Y_{k}} + 0.04570}{Y_{k}}} \\ {\zeta = \quad {{0.918221} - X_{k} - \frac{Y_{k}}{Y_{k}}}} \\ {{{and}\text{:}}\quad} \\ {\xi_{D} = \quad \frac{{0.48105X_{D}} + {0.78841Y_{D}} - 0.08081}{Y_{D}}} \\ {\eta_{D} = \quad \frac{{{- 0.27200}X_{D}} + {1.11962Y_{D}} + 0.04570}{Y_{D}}} \\ {\zeta_{D} = \quad {{0.918221} - X_{D} - \frac{Y_{D}}{Y_{D}}}} \end{matrix}$

[0099]  X_(D), Y_(D) are the trichromatic coordinates of the reference source. Here, the reference source is chosen to be identical to the D₆₅ light source, for which ξ_(D)=η_(D)=ξ_(D)=1.

[0100] R₀, G₀, B₀ and R_(0D), G_(0D), B_(0D) are the coordinates in the RGB system of the test source and the D₆₅ light source, characteristic of the chromatic adaptation: ${\begin{matrix} R_{0} \\ G_{0} \\ B_{0} \end{matrix}} = {{0.2\frac{E_{0}}{\pi}{\begin{matrix} \xi \\ \eta \\ \zeta \end{matrix}}\quad {and}\quad {\begin{matrix} R_{0D} \\ V_{0D} \\ B_{0D} \end{matrix}}} = {0.2\frac{E_{0}}{\pi}{\begin{matrix} \xi_{D} \\ \eta_{D} \\ \zeta_{D} \end{matrix}}}}$

[0101] where E₀ and E_(0D) are the respective luminances of the test source and the D₆₅ light source, such as E₀=E_(0D)=1 000 lux, and the factor 0.2 is the luminance factor of gray.

[0102] The functions β are defined by the following equations: $\begin{matrix} {{\beta_{1}\left( R_{0} \right)} = \frac{6.469 + {6.362R_{0}^{0.4495}}}{6.469 + R_{0}^{0.4495}}} \\ {{\beta_{1}\left( G_{0} \right)} = \frac{6.469 + {6.362G_{0}^{0.4495}}}{6.469 + G_{0}^{0.4495}}} \\ {{\beta_{2}\left( B_{0} \right)} = \frac{8.414 + {8.0911B_{0}^{0.5128}}}{8.414 + B_{0}^{0.5128}}} \\ {{\beta_{1}\left( R_{0D} \right)} = {{\beta_{1}\left( G_{0D} \right)} = 3.6810}} \\ {{\beta_{2}\left( B_{0D} \right)} = 3.5656} \end{matrix}$

[0103] f) Converting from the spectral coordinates R_(Di), G_(Di), B_(Di) of the RGB system to the trichromatic coordinates X_(Di), Y_(Di), Z_(Di) using the following equations:

X _(Di)=1.85995R _(Di)−1.12939G _(Di)+0.21990B _(Di)

Y _(Di)=0.36119R _(Di)+0.63881G _(Di)

Z _(Di)=1.08906B _(Di)

[0104] g) Converting from the trichromatic coordinates X_(Di), Y_(Di), Z_(Di) to the coordinates a*_(ki), a*_(ki), b*_(ki) in the space CIELAB, as defined by the International Commission on Illumination, using the following equations: $\begin{matrix} {L_{ki}^{*} = \quad {{116\left( \frac{Y_{Di}}{Y_{n}} \right)^{\frac{1}{3}}} - 16}} & {\quad {{{if}\quad \frac{Y_{Di}}{Y_{n}}} > 0.008856}} \\ {L_{ki}^{*} = \quad {903.3\left( \frac{Y_{Di}}{Y_{n}} \right)}} & {\quad {{{if}\quad \frac{Y_{Di}}{Y_{n}}} \leq 0.008856}} \\ {a_{ki}^{*} = \quad {500\left\lbrack {{f\left( \frac{X_{Di}}{X_{n}} \right)} - {f\left( \frac{Y_{Di}}{Y_{n}} \right)}} \right\rbrack}} & \quad \\ {b_{ki}^{*} = \quad {200\left\lbrack {{f\left( \frac{Y_{Di}}{Y_{n}} \right)} - {f\left( \frac{Z_{Di}}{Z_{n}} \right)}} \right\rbrack}} & \quad \end{matrix}$

[0105]  in which the functions f are defined as follows: $\begin{matrix} {{f\left( \frac{X}{X_{n}} \right)} = \quad \left( \frac{X}{X_{n}} \right)^{\frac{1}{3}}} & {\quad {{{if}\quad \frac{X}{X_{n}}} > 0.008856}} \\ {{f\left( \frac{X}{X_{n}} \right)} = \quad {{7,787\left( \frac{X}{X_{n}} \right)} + \frac{16}{116}}} & {\quad {{{if}\quad \frac{X}{X_{n}}} \leq 0.008856}\quad} \\ {{f\left( \frac{Y}{Y_{n}} \right)} = \quad \left( \frac{Y}{Y_{n}} \right)^{\frac{1}{3}}} & {\quad {{{if}\quad \frac{Y}{Y_{n}}} > 0.008856}} \\ {{f\left( \frac{Y}{Y_{n}} \right)} = \quad {{7,787\left( \frac{Y}{Y_{n}} \right)} + \frac{16}{116}}} & {\quad {{{if}\quad \frac{Y}{Y_{n}}} \leq 0.008856}\quad} \\ {{f\left( \frac{Z}{Z_{n}} \right)} = \quad \left( \frac{Z}{Z_{n}} \right)^{\frac{1}{3}}} & {\quad {{{if}\quad \frac{Z}{Z_{n}}} > 0.008856}} \\ {{f\left( \frac{Z}{Z_{n}} \right)} = \quad {{7,787\left( \frac{Z}{Z_{n}} \right)} + \frac{16}{116}}} & {\quad {{{if}\quad \frac{Z}{Z_{n}}} \leq 0.008856}\quad} \end{matrix}$

[0106] X_(n), Y_(n), Z_(n) are the trichromatic coordinates of the color white when illuminated by the D₆₅ light source.

[0107] The calculations of steps c) through g) are effected for each sample of the test palette, and for perfect white if it is not included in the test palette.

[0108] The space CIELAB has the advantage of being uniform for human vision. The axis L* represents the value, from 0 for black to 100 for perfect white, and the axes a* and b* represent the chromaticity, respectively for the pairs of opposites green (a*=−100)−red (a*=+100) and blue (b*=−100)−yellow (b*=100).

[0109] The above calculations are also effected to measure the real color of the samples, steps c) through g) being repeated for each sample of the test palette and for the perfect white, each illuminated by the ideal source (i.e. the D₆₅ light source). L^(*) _(id,i), a^(*) _(id,i), b^(*) _(id,i) are the coordinates of the colors of the samples of the test palette in the space CIELAB when illuminated by a white source.

[0110] It is then possible to obtain, in the CIELAB system and for each of the colors i, a so-called deviation vector characteristic of the calorimetric deviation (FIG. 8) and having the following coordinates:

L ^(*) _(vi) =L ^(*) _(ki) −L _(id,i)

a ^(*) _(vi) =a ^(*) _(ki) −a _(id,i) ^(*)

b ^(*) _(vi) =b ^(*) _(ki) −b _(id,i) ^(*)

[0111] The deviation vector is then corrected to compensate for chromatic adaptation, by subtracting the deviation vector of perfect white from the deviation vector of each sample of the test palette.

[0112] A corrected deviation vector is therefore obtained for each sample of the test palette with coordinates L^(*) _(ci), a^(*) _(ci), b^(*) _(ci) in the space CIELAB, such as:

L ^(*) _(ci) =L ^(*) _(vi) −L ^(*) _(vwhite)

a ^(*) _(ci) =a ^(*) _(vi) −a ^(*) _(vwhite)

b ^(*) _(vi) =b ^(*) _(vi) −b ^(*) _(vwhite)

[0113] in which L^(*) _(vwhite), a^(*) _(vwhite), b^(*) _(vwhite) are the coordinates in the CIELAB space of the deviation vector of perfect white.

[0114] The coordinates of the corrected deviation vector thus constitute a measurement, for each sample i of the test palette, of the calorimetric deviation caused by the test source, allowing for chromatic adaptation.

[0115] The chromatic error ΔE^(*) _(ab,i) for each sample i is equal to the modulus of the corrected deviation vector:

ΔE ^(*) _(ab,i) ={square root}{square root over (L^(*2) _(ci)+a^(*) _(ci)+b^(*) _(ci))}

[0116] In a different embodiment, no account is taken of value variations, but only of chromaticity, so that the chromatic error is defined by the modulus of the projection of the corrected deviation vector in the space a* b*:

ΔE ^(*) _(ab,i) ={square root}{square root over (a^(*hd ci)+b^(*) _(ci))}

[0117] The mean chromatic error ΔE^(*) _(m), is then calculated; it is equal to the arithmetical mean of all the chromatic errors ΔE^(*) _(ab,i): ${\Delta \quad E_{m}^{*}} = {\frac{1}{N}{\sum\limits_{i = 1}^{N}\quad {\Delta \quad E_{{ab},i}^{*}}}}$

[0118] The value of the mean chromatic error ΔE^(*) _(m), is then compared to a predetermined test value ΔE_(o), which constitutes a first criterion for acceptance of the test color from the range.

[0119] Accordingly, if the value of the global chromatic error ΔE^(*) _(m) is less than or equal to the test value ΔE_(o), the test color is accepted, i.e. added to the range.

[0120] In one embodiment of the invention, the test value ΔE_(o) is chosen to be equal to 10. It is preferably chosen to be equal to 5.

[0121] If the value of the global chromatic error ΔE^(*) _(m) exceeds the test value ΔE_(o), then the test color is refused, i.e. excluded from the range.

[0122] As an alternative to this, the test color is not refused at this stage. Instead, the angular distribution of the calorimetric deviation in the space a* b* is measured.

[0123] To this end, a deviation angle is measured for each sample i, formed by the projection in the space a* b* of the corrected deviation vector with the axis a* or the axis b*. The value θ_(vi) of this angle is provided for the axis a* by the following equation: $\theta_{vi} = {{Arctan}\frac{b_{ci}^{*}}{a_{ci}^{*}}}$

[0124] and that for the axis b* by the following equation: $\theta_{vi} = {{Arctan}\frac{a_{ci}^{*}}{b_{ci}^{*}}}$

[0125] The arithmetic mean of the angular distribution is then calculated, i.e. all of the deviation angles, followed by the standard deviation of the angular distribution, the standard deviation providing the measurement referred to above of the angular distribution. If the angular distribution is uniform, the test color is accepted. Otherwise, it is refused.

[0126] In one embodiment, the angular distribution is declared uniform if its standard deviation is less than 60°, preferably less than 55°.

[0127]FIG. 11 shows the a* b* space into which have been transferred, as shown by circles, the coordinates of 127 colors of the test palette previously defined for the first embodiment, when illuminated by the D₆₅ light source, and, as shown by crosses, their coordinates when illuminated by the test source formed by the D₆₅ light source filtered by a glass whose color is characterized by the spectral energy distribution shown in FIG. 6, taking account of chromatic adaptation.

[0128]FIG. 10 shows the a* b* space into which have been transferred, as shown by circles, the coordinates of six eigencolors of the test palette previously defined in the second embodiment, when illuminated by the D₆₅ light source, and, as shown by crosses, their coordinates when illuminated by the test source formed of the D₆₅ light source, assumed to be filtered by the same lens as above and taking account of chromatic adaptation.

[0129] This figure also shows, as arrows, the six associated corrected deviation vectors, connecting the circles to the crosses. For each eigencolor, the associated chromatic error in the a* b* space is equal to the length of the corresponding corrected deviation vector.

[0130] In a different embodiment of the invention, the first criterion for accepting the test color is based on the mean color rendition index R96_(a) of the test source, compared to a test value R96₀.

[0131] The mean color rendition index R96_(a) is given by the following equation: ${{R96}_{a} = {\frac{1}{N}{\sum\limits_{i = 1}^{6}\quad {R96}_{i}}}},$

[0132] in which R96₁ is the color rendition index for the test source for each color i of the test palette, in turn supplied by the following equation:

R96_(i)=100−cΔE ^(*) _(ab,i)

[0133] where c=3.2562.

[0134] The test value R96₀ is chosen to be equal to 85, for example, or preferably 90.

[0135] The FIG. 12 diagram illustrates the principle of accepting or refusing a test color for the range.

[0136] It is therefore possible to constitute a range of colors from a predetermined set by repeating the above operations until the number of colors required for the range is obtained.

[0137] That number is left to the judgement of the person skilled in the art; nevertheless, to provide a concrete example, it is possible to constitute a range of colors whose hues are separate: for example six colors with fundamental hues: a green, a blue, a purple, a red, an orange, a yellow, or a range of colors with the same hue but different chromas and values: for example, a dozen blues of greater or lesser chroma and brightness.

[0138] Once the required final color of the lens is known, it is obtained by mixing primary coloring agents. In one embodiment of the invention the concentration of each primary coloring agent is calculated using the subtractive mixing method well known to the person skilled in the art. It is then possible to manufacture the lens, after selecting its color from the color range established in the manner previously described.

[0139] Three acceptable test colors are provided at present, with respective gray, green and brown hues, and which thus form a range as defined by the invention.

[0140] Each color can be characterized by the spectral distribution of its transmission factor τ1(λ), expressed as a percentage and as a function of the wavelength λ of the incendent light, expressed in nanometers (nm).

[0141] The respective spectral distributions of the three colors of gray, green and brown hue previously cited and respectively denoted GRAY, GREEN and BROWN, are given by the following tables of values. GRAY Wavelength Transmission factor λ (nm) τ 1 (%) 350 0.151694625 351 0.206969129 352 0.263616063 353 0.341560226 354 0.435973016 355 0.595800287 356 0.785995527 357 0.996956708 358 1.298629716 359 1.649411527 360 2.144257282 361 2.711832274 362 3.419099229 363 4.028315894 364 4.685020735 365 5.430495265 366 6.247534403 367 7.168632636 368 8.027566852 369 9.254469087 370 10.6302534 371 12.08396857 372 13.55805465 373 14.95109773 374 16.17059236 375 17.46510848 376 18.70391852 377 19.83943138 378 20.93915208 379 22.01115257 380 23.01171396 381 23.93718868 382 24.79082183 383 25.54678394 384 26.24337578 385 26.90313523 386 27.51481596 387 28.06856778 388 28.59218398 389 29.08606938 390 29.40466351 391 29.80119144 392 30.15091518 393 30.55737226 394 30.84917168 395 31.10049734 396 31.42079566 397 31.61423652 398 31.88712611 399 32.24008281 400 32.41756083 401 32.65591012 402 32.93345185 403 33.21313361 404 33.38474983 405 33.6823143 406 34.13360388 407 34.32195772 408 34.5226446 409 34.86624106 410 35.21047366 411 35.58333449 412 35.80562537 413 36.16191166 414 36.46660816 415 36.79931779 416 37.15259937 417 37.47971435 418 37.76879932 419 37.99422901 420 38.30384897 421 38.68958152 422 39.0879526 423 39.42111231 424 39.72176954 425 40.13693778 426 40.46828425 427 40.70035149 428 41.13468931 429 41.31302158 430 41.74417977 431 42.33024774 432 42.67726419 433 42.82709685 434 43.3014327 435 43.63963746 436 44.00318533 437 44.37853157 438 44.62371228 439 45.08605578 440 45.31633393 441 45.61595221 442 46.05367317 443 46.29031653 444 46.61029233 445 46.88674368 446 47.11856161 447 47.40926976 448 47.60027302 449 47.83309781 450 48.19463075 451 48.44163701 452 48.64160583 453 48.83596531 454 49.00828107 455 49.28087968 456 49.54683384 457 49.67233092 458 49.90838573 459 50.14468141 460 50.40367427 461 50.66444983 462 50.74929703 463 50.71988507 464 50.84790673 465 50.99842038 466 51.2557445 467 51.2577705 468 51.26857718 469 51.39753233 470 51.34699382 471 51.27015335 472 51.1108684 473 51.13983328 474 51.17005058 475 51.16589324 476 51.0857339 477 51.05343627 478 51.06375135 479 51.02306375 480 51.04245077 481 51.10738923 482 51.12523652 483 51.13230981 484 51.28828273 485 50.81754489 486 51.73928913 487 52.21340557 488 51.74542471 489 51.78179865 490 51.90657325 491 51.98779226 492 51.9865365 493 52.01359901 494 52.12920118 495 52.11340653 496 51.91227268 497 52.04387546 498 51.78941768 499 51.7382666 500 51.50158588 501 51.19095477 502 50.91651083 503 50.65877615 504 50.35842556 505 50.01755161 506 49.59973921 507 49.24474856 508 48.82181173 509 48.56689424 510 48.15369141 511 47.88406813 512 47.62139199 513 47.44968041 514 47.34778256 515 47.22878071 516 47.15106189 517 47.15644627 518 47.23500375 519 47.42218076 520 47.59379283 521 47.66522807 522 47.96847225 523 48.16786285 524 48.42036693 525 48.60925228 526 48.87254774 527 49.14029069 528 49.28120433 529 49.44455809 530 49.52475222 531 49.60071947 532 49.62316186 533 49.59886788 534 49.49485439 535 49.39344518 536 49.23155757 537 48.93622997 538 48.64513078 539 48.33675979 540 47.91088874 541 47.48699707 542 47.06437534 543 46.61438661 544 46.11935334 545 45.63428679 546 45.11794672 547 44.62410424 548 44.28916116 549 43.90174713 550 43.48533873 551 43.1531623 552 42.94962397 553 42.81261641 554 42.70126215 555 42.63923257 556 42.74779661 557 42.81355655 558 42.99463521 559 43.15003531 560 43.37728285 561 43.73403514 562 44.06777974 563 44.34989006 564 44.67793363 565 45.06239974 566 45.36292896 567 45.65864409 568 45.94024409 569 46.13039355 570 46.45548625 571 46.65739818 572 46.86574468 573 46.88149305 574 46.99249908 575 47.19114882 576 47.19394685 577 46.95289021 578 47.3254339 579 47.06199836 580 47.00364509 581 46.62513578 582 47.13532647 583 46.92155686 584 46.37364251 585 46.44967191 586 46.43447646 587 46.09738207 588 46.04366239 589 45.95426868 590 45.73932639 591 45.53788741 592 45.21593932 593 45.1646353 594 45.14272233 595 44.91737024 596 44.89005672 597 44.6244962 598 44.36907978 599 44.40777666 600 44.27282529 601 44.196962 602 44.02937912 603 43.89345712 604 43.93096743 605 43.749884 606 43.70830499 607 43.65113846 608 43.59031343 609 43.49422022 610 43.48018257 611 43.45727368 612 43.43151561 613 43.3816647 614 43.39309771 615 43.39900595 616 43.42522152 617 43.41149212 618 43.5309114 619 43.46557676 620 43.47588623 621 43.56591149 622 43.56093708 623 43.68786608 624 43.77621539 625 43.82507612 626 43.9202607 627 43.94129079 628 44.08510482 629 44.1257826 630 44.29275976 631 44.39636878 632 44.54695426 633 44.69196542 634 44.8248476 635 44.90642312 636 45.03925063 637 45.27147674 638 45.45636261 639 45.6852214 640 45.8154225 641 46.04669573 642 46.27598614 643 46.42835889 644 46.66241878 645 46.90322007 646 47.28533674 647 47.51015231 648 47.71015217 649 47.96383775 650 48.35300247 651 48.62911032 652 48.95009426 653 49.18466089 654 49.69360534 655 48.72220946 656 50.01897947 657 51.63668291 658 51.19792472 659 51.51968397 660 51.92390148 661 52.40730449 662 52.82579372 663 53.250548 664 53.70159 665 54.21142272 666 54.75434387 667 55.21557701 668 55.72717749 669 56.23388555 670 56.88980521 671 57.4152792 672 57.96915171 673 58.59845449 674 59.20272925 675 59.82229886 676 60.43972495 677 61.0708989 678 61.71923469 679 62.4106236 680 63.07013506 681 63.73367667 682 64.40349207 683 65.06205693 684 65.73038704 685 66.40835304 686 67.13973722 687 67.80513555 688 68.48915906 689 69.15168103 690 69.83594554 691 70.45763269 692 71.11451866 693 71.79344999 694 72.47711238 695 73.08169843 696 73.71609041 697 74.25531403 698 74.98942093 699 75.56317601 700 76.15018309 701 76.73062887 702 77.2800235 703 77.88584058 704 78.39305198 705 78.94308092 706 79.39334283 707 79.94354339 708 80.50621887 709 80.9474412 710 81.39054552 711 81.90313287 712 82.357979 713 82.75118097 714 83.21128488 715 83.63390107 716 84.01400576 717 84.40213929 718 84.73901662 719 85.14040798 720 85.48849151 721 85.82744317 722 86.18193118 723 86.46627167 724 86.74945482 725 86.98866418 726 87.32800248 727 87.60650485 728 87.78617616 729 88.07155469 730 88.27097983 731 88.52876931 732 88.77113065 733 88.95123717 734 89.1350365 735 89.39201228 736 89.53188533 737 89.73757296 738 89.91727084 739 90.02889977 740 90.21393536 741 90.41761595 742 90.47799515 743 90.68127628 744 90.79764191 745 90.95888721 746 91.06281034 747 91.14343243 748 91.28544459 749 91.38954014 750 91.49797365 GREEN Wavelength Transmission factor λ (nm) τ 2 (%) 350 0.14899478 351 0.19307862 352 0.24360347 353 0.33157605 354 0.40496553 355 0.51783277 356 0.67949269 357 0.87017322 358 1.11154255 359 1.41152548 360 1.78640852 361 2.16875379 362 2.70765511 363 3.16741351 364 3.636577 365 4.18171185 366 4.70786397 367 5.26999667 368 5.81153436 369 6.60475396 370 7.47641614 371 8.3472809 372 9.18857687 373 10.0106778 374 10.7023235 375 11.3986217 376 12.0003543 377 12.5758093 378 13.1024492 379 13.6240115 380 14.1031715 381 14.4542339 382 14.7753096 383 15.0952945 384 15.3456935 385 15.5457361 386 15.764406 387 15.9427868 388 16.0713303 389 16.1868993 390 16.272397 391 16.3476451 392 16.4424384 393 16.5666412 394 16.6134177 395 16.6486598 396 16.7674231 397 16.7616802 398 16.8440356 399 16.9610638 400 16.9747009 401 17.1297607 402 17.187447 403 17.3210806 404 17.469251 405 17.6123063 406 17.7924419 407 17.9129909 408 18.0896066 409 18.2994007 410 18.5403897 411 18.7487821 412 18.9380044 413 19.2306815 414 19.4752085 415 19.7351487 416 20.0198245 417 20.3374809 418 20.5851845 419 20.8798293 420 21.2136468 421 21.5152082 422 21.861776 423 22.2446301 424 22.5797307 425 22.9276314 426 23.3278195 427 23.6837618 428 24.0859321 429 24.4789616 430 24.9403236 431 25.4087629 432 25.8252495 433 26.2744558 434 26.7210878 435 27.147935 436 27.6901073 437 28.1609272 438 28.5985261 439 29.1439297 440 29.5833534 441 30.054603 442 30.6084791 443 31.057911 444 31.5359559 445 32.0118676 446 32.4406334 447 32.9517537 448 33.427884 449 33.8333898 450 34.3090722 451 34.7434969 452 35.1686688 453 35.6107715 454 36.0525729 455 36.4690106 456 36.8558461 457 37.2340277 458 37.6691576 459 38.0863662 460 38.4576615 461 38.9015382 462 39.2319029 463 39.5854087 464 39.9754434 465 40.3093512 466 40.7465844 467 40.9953685 468 41.4032957 469 41.7466548 470 42.0170429 471 42.344472 472 42.6012348 473 42.9489638 474 43.2614199 475 43.5258454 476 43.767853 477 44.0449481 478 44.3521301 479 44.5409876 480 44.8026076 481 45.0572545 482 45.2758511 483 45.4847199 484 45.7471614 485 45.7586149 486 46.3026178 487 46.4634439 488 46.4832419 489 46.7030133 490 46.8952901 491 47.0246026 492 47.197056 493 47.3119259 494 47.4689605 495 47.5167255 496 47.5734174 497 47.6989434 498 47.6719274 499 47.7640331 500 47.7543845 501 47.735303 502 47.7096283 503 47.6910883 504 47.6460775 505 47.6115632 506 47.4934627 507 47.4177032 508 47.3083937 509 47.2184108 510 47.067786 511 46.9586644 512 46.8626574 513 46.7594531 514 46.6627262 515 46.5158147 516 46.4508959 517 46.3055665 518 46.1240122 519 46.0471002 520 45.9374195 521 45.7574091 522 45.6946525 523 45.4888152 524 45.3986045 525 45.2766465 526 45.1111111 527 44.9594083 528 44.7572761 529 44.5661314 530 44.4088493 531 44.1531159 532 43.9334757 533 43.6963092 534 43.3973859 535 43.1504143 536 42.8975001 537 42.5630841 538 42.2483419 539 41.9269957 540 41.5564116 541 41.2197762 542 40.9003252 543 40.5401509 544 40.1746783 545 39.8090036 546 39.4729125 547 39.0761951 548 38.8202138 549 38.4691483 550 38.1275366 551 37.8077999 552 37.5343205 553 37.2489933 554 37.0118894 555 36.7552229 556 36.5656382 557 36.3238696 558 36.1707271 559 35.9319641 560 35.7946194 561 35.6751869 562 35.5132357 563 35.3567554 564 35.2486901 565 35.1682054 566 35.0333185 567 34.9110594 568 34.777617 569 34.6281038 570 34.5359137 571 34.4181112 572 34.2933298 573 34.1214634 574 34.0253915 575 33.9123835 576 33.7625863 577 33.5288209 578 33.5671286 579 33.2855623 580 33.1847747 581 32.9114019 582 33.0096195 583 32.7836591 584 32.5141618 585 32.4688555 586 32.3399896 587 32.1615944 588 32.0665338 589 31.9665592 590 31.8331153 591 31.7239748 592 31.5678965 593 31.5493933 594 31.4798439 595 31.4061716 596 31.3972074 597 31.3412734 598 31.2863322 599 31.3619959 600 31.3370067 601 31.3998274 602 31.4277652 603 31.5020415 604 31.662939 605 31.7204222 606 31.8503161 607 31.9980224 608 32.1666797 609 32.3307588 610 32.515804 611 32.7023392 612 32.924124 613 33.1098751 614 33.3539738 615 33.5910931 616 33.8397798 617 34.0826728 618 34.3604925 619 34.5728665 620 34.8513144 621 35.0580218 622 35.2900476 623 35.5877886 624 35.8437007 625 36.1193737 626 36.431951 627 36.6804796 628 36.9934445 629 37.2255254 630 37.5639218 631 37.8804315 632 38.1980143 633 38.5425426 634 38.889666 635 39.2333675 636 39.5763694 637 39.9570132 638 40.300589 639 40.6957043 640 41.0578917 641 41.4476875 642 41.7715054 643 42.1504863 644 42.6101229 645 42.989726 646 43.4678675 647 43.8723536 648 44.3154279 649 44.7639598 650 45.1800105 651 45.696258 652 46.1773186 653 46.6727691 654 47.27973 655 46.9639237 656 47.9617313 657 48.7063775 658 49.1300405 659 49.742735 660 50.2458676 661 50.7671308 662 51.3741746 663 51.9407793 664 52.508444 665 53.1365429 666 53.6787176 667 54.3030447 668 54.937046 669 55.5108772 670 56.1509649 671 56.7162993 672 57.3357784 673 57.981628 674 58.5902197 675 59.2053294 676 59.8437151 677 60.484734 678 61.1064475 679 61.7416012 680 62.4034975 681 63.0438262 682 63.6886275 683 64.2977932 684 64.9427265 685 65.5499235 686 66.2175939 687 66.8509486 688 67.4736163 689 68.0841405 690 68.7016976 691 69.3008077 692 69.9165028 693 70.5310077 694 71.1513823 695 71.7272665 696 72.2952691 697 72.827298 698 73.4454489 699 74.000728 700 74.5554574 701 75.121768 702 75.6159603 703 76.1598824 704 76.6686481 705 77.1813209 706 77.6353421 707 78.1213633 708 78.6268279 709 79.0806691 710 79.5056979 711 79.9721631 712 80.3767398 713 80.7940075 714 81.2139765 715 81.6058381 716 81.9891475 717 82.3541812 718 82.6603735 719 83.0517364 720 83.3927457 721 83.7193433 722 84.0213856 723 84.3078539 724 84.6224249 725 84.8749638 726 85.180053 727 85.4629646 728 85.6781166 729 85.9322964 730 86.1605488 731 86.4023082 732 86.6624425 733 86.8672604 734 87.0488562 735 87.2892745 736 87.486352 737 87.6877254 738 87.8920713 739 88.0371366 740 88.2031634 741 88.4257963 742 88.5351848 743 88.6953337 744 88.8668948 745 89.0120054 746 89.1366024 747 89.2584337 748 89.3874976 749 89.4856952 750 89.5900992 BROWN Wavelength Transmission factor λ (nm) τ 3 (%) 350 0.11858921 351 0.13166479 352 0.16038578 353 0.23249626 354 0.27983577 355 0.36079104 356 0.4728814 357 0.59939854 358 0.77679339 359 0.99369353 360 1.27734152 361 1.61186549 362 2.04253813 363 2.42335776 364 2.86878412 365 3.33963348 366 3.77023423 367 4.3092558 368 4.79261464 369 5.50546723 370 6.34038223 371 7.21308281 372 8.08238191 373 8.96985643 374 9.89080474 375 10.8286786 376 11.6565823 377 12.4568832 378 13.2412847 379 14.0192782 380 14.6892566 381 15.3218539 382 15.9272154 383 16.4782225 384 16.9699677 385 17.4163164 386 17.7949036 387 18.1668341 388 18.5001275 389 18.7074921 390 18.8941402 391 19.0895239 392 19.2080179 393 19.2989176 394 19.2688944 395 19.3036646 396 19.2781208 397 19.2290768 398 19.161256 399 19.0504117 400 18.8822778 401 18.803454 402 18.7049864 403 18.5849834 404 18.4474311 405 18.3687688 406 18.2828524 407 18.1713027 408 18.1441891 409 18.1173547 410 18.0811078 411 18.0555958 412 18.0401395 413 18.0546839 414 17.9979201 415 18.0101761 416 18.0347527 417 18.0166633 418 18.0253693 419 17.9717362 420 18.0062612 421 17.962425 422 17.9324726 423 17.8658506 424 17.8125356 425 17.7665179 426 17.7037389 427 17.6566451 428 17.5735579 429 17.4887108 430 17.3864347 431 17.2845669 432 17.1391296 433 17.1572421 434 17.0942134 435 16.8795446 436 16.8743191 437 16.7952083 438 16.7013882 439 16.6483674 440 16.5415587 441 16.5337872 442 16.4482887 443 16.3959633 444 16.3489375 445 16.2586814 446 16.2323184 447 16.1821725 448 16.2070659 449 16.1776958 450 16.1980643 451 16.1621789 452 16.2146482 453 16.1979932 454 16.2273289 455 16.3275904 456 16.354539 457 16.4361933 458 16.4835063 459 16.5563855 460 16.6086393 461 16.7347957 462 16.9084438 463 17.056792 464 17.2067819 465 17.2716668 466 17.4274109 467 17.5118452 468 17.7162613 469 17.8460494 470 18.0041262 471 18.2116891 472 18.3724398 473 18.5581491 474 18.6781839 475 18.8489702 476 18.95756 477 19.0886436 478 19.2995533 479 19.4346233 480 19.6500891 481 19.7765787 482 19.9317434 483 20.1206623 484 20.288192 485 20.6073913 486 20.6250019 487 20.3658146 488 20.790384 489 21.1197567 490 21.3134294 491 21.4676373 492 21.594016 493 21.7281515 494 21.8641765 495 21.9306297 496 22.024497 497 22.0263349 498 22.0210634 499 22.102889 500 22.0013428 501 21.951974 502 21.8665292 503 21.7617198 504 21.5515234 505 21.3937531 506 21.2250628 507 21.030669 508 20.8390623 509 20.6036357 510 20.3583922 511 20.1866033 512 19.9695514 513 19.8144839 514 19.646508 515 19.4991722 516 19.471189 517 19.3716917 518 19.3056146 519 19.3503491 520 19.3265259 521 19.4067327 522 19.5184929 523 19.6353374 524 19.7723232 525 19.940105 526 20.1694556 527 20.3378381 528 20.5424665 529 20.7580405 530 20.9180576 531 21.135995 532 21.3325334 533 21.5504822 534 21.6538938 535 21.8244587 536 21.9292813 537 22.0271088 538 22.1271218 539 22.1558081 540 22.194423 541 22.2017835 542 22.1834598 543 22.1069179 544 22.0132311 545 21.9009364 546 21.8292997 547 21.7510182 548 21.6495672 549 21.4886725 550 21.4358406 551 21.3524047 552 21.3177825 553 21.2828426 554 21.2663981 555 21.3390458 556 21.4084155 557 21.496507 558 21.6314618 559 21.8175587 560 22.070006 561 22.3071447 562 22.5355952 563 22.8371353 564 23.1686425 565 23.491546 566 23.8105302 567 24.153144 568 24.4388405 569 24.7890799 570 25.0389891 571 25.3006387 572 25.530969 573 25.758305 574 26.0789036 575 26.194495 576 26.3893492 577 26.6113525 578 26.8614002 579 26.7683648 580 27.1018325 581 27.2391193 582 27.4257801 583 27.1930411 584 27.5421999 585 27.7770123 586 27.6404133 587 27.8335521 588 27.9701843 589 28.0172717 590 28.23734 591 28.3816253 592 28.6224 593 28.931722 594 29.0533222 595 29.4171928 596 29.688389 597 30.0602793 598 30.408636 599 30.8234404 600 31.113066 601 31.4879328 602 31.7784982 603 32.1418257 604 32.394647 605 32.5610329 606 32.7525741 607 32.8649647 608 32.9391656 609 32.9121246 610 32.8995517 611 32.6836018 612 32.5185174 613 32.2178604 614 31.9006431 615 31.5463452 616 31.1355519 617 30.7172219 618 30.3530635 619 29.8225983 620 29.4024682 621 28.8365813 622 28.4184825 623 27.9870185 624 27.5590186 625 27.2083918 626 27.0242194 627 26.7628987 628 26.5097509 629 26.239054 630 26.0271855 631 25.8558343 632 25.730378 633 25.6902366 634 25.6957093 635 25.7386851 636 25.8415304 637 25.9609718 638 26.0699715 639 26.2823614 640 26.5294925 641 26.8863035 642 27.2796441 643 27.8484082 644 28.4768282 645 29.230904 646 30.0941614 647 31.0451601 648 32.2134743 649 33.4348582 650 34.8208685 651 36.2431583 652 37.9256264 653 39.664852 654 41.491307 655 43.3837605 656 45.4567619 657 45.9886925 658 49.1678149 659 51.6650382 660 53.844941 661 56.0419479 662 58.065722 663 60.1373501 664 62.1300327 665 64.1057763 666 65.9598517 667 67.7418849 668 69.5076223 669 71.1267003 670 72.7218255 671 74.1091946 672 75.5079414 673 76.7988993 674 77.9267277 675 79.0166166 676 80.0250398 677 80.9552627 678 81.8254735 679 82.642224 680 83.3570442 681 84.0293196 682 84.6553221 683 85.1452691 684 85.6318462 685 86.1236624 686 86.6129777 687 86.928132 688 87.2450077 689 87.553425 690 87.8359252 691 88.0901228 692 88.3596072 693 88.5721315 694 88.8050556 695 88.9254574 696 89.1009854 697 89.2429507 698 89.459957 699 89.5684612 700 89.6611477 701 89.7598431 702 89.8629883 703 90.001029 704 90.095548 705 90.1464078 706 90.1570979 707 90.223841 708 90.4209914 709 90.4213885 710 90.3898233 711 90.4517729 712 90.4706442 713 90.4970706 714 90.5925084 715 90.6100163 716 90.6454402 717 90.6627592 718 90.6133989 719 90.6490232 720 90.6181745 721 90.6233484 722 90.5992724 723 90.6102153 724 90.5734128 725 90.5813689 726 90.5976809 727 90.6784885 728 90.6040473 729 90.6006651 730 90.6026546 731 90.5915138 732 90.7097561 733 90.6404641 734 90.6225524 735 90.707565 736 90.6892418 737 90.7270874 738 90.7892682 739 90.6862546 740 90.7368501 741 90.8177819 742 90.7153336 743 90.7187202 744 90.759169 745 90.6872503 746 90.7420308 747 90.6593748 748 90.7332637 749 90.6844624 750 90.6486251

[0142] The spectral distributions of the transmission factors of the colors GRAY, GREEN and BROWN are shown in the FIG. 13, 14 and 15 graphs, respectively.

[0143] The mean chromatic error values ΔE^(*) _(m) of the colors GRAY, GREEN and BROWN for the calorimetric deviation caused by a test palette of 127 samples defined in accordance with the first embodiment of the invention described above are respectively equal to 0.58945, 2.4204 and 3.4606.

[0144] If the test value ΔE_(o) is chosen to be equal to 5, it is found that the values of these mean chromatic errors are all less than the test value, and so the colors GRAY, GREEN and BROWN are accepted.

[0145] However, if the test value ΔE_(o) is instead chosen to be less than 5, for example equal to 0.5, it is necessary to measure the angular distribution corresponding to each of these colors.

[0146] Calculated in the manner previously defined, for the axis a* of the space CIELAB, the standard deviations of the GRAY, GREEN and BROWN colors are respectively equal to 51.454°, 40.622° and 36.901°, and are therefore all less than 55°. The. angular distribution is therefore uniform for each of these colors. 

There is claimed:
 1. A method of obtaining a range of colors, including the following steps: selecting a test color from a predetermined set of colors, selecting a test palette comprising a plurality of color samples, measuring the real color of each sample when illuminated by a white light source, measuring the apparent color of each sample when illuminated by a test source formed by said white light source filtered by said test color, measuring the chromatic error between the real color and the apparent color of each sample, taking account of chromatic adaptation, measuring the mean chromatic error for all the chromatic errors, comparing the mean chromatic error to a test value, and adding the test color to the range if the mean chromatic error is less than or equal to said test value.
 2. The method claimed in claim 1 wherein said test color is added to said range if and only if each chromatic error is less than or equal to said test value.
 3. A method claimed in claim 1, which includes the following steps if at least one chromatic error is greater than said test value: measuring the angular distribution of the calorimetric deviations between the real color and the apparent color of each sample, and adding said test color to said range if said angular distribution is uniform.
 4. The method claimed in claim 1 wherein said set comprises the Munsell atlas.
 5. The method claimed in claim 1 wherein said test palette comprises a plurality of color samples chosen from the Munsell atlas.
 6. The method claimed in claim 1 wherein said test palette comprises a plurality of samples whose colors are most representative of the Munsell space.
 7. The method claimed in claim 1 wherein said apparent color and said real color are measured by calculating their coordinates in a predetermined chromatic space.
 8. The method claimed in claim 7 wherein said chromatic space is the CIELAB space.
 9. A range of more than two colors obtained by the method claimed in any of claims 1 to
 8. 10. A method of obtaining a colored ophthalmic lens, including a step of selecting a color from a range as claimed in claim 9 or obtained by a method as claimed in any of claims 1 to
 8. 